Ion implantation has become the technology preferred by industry to dope semiconductors with impurities in the large-scale manufacture of integrated circuits. High-energy ion implanters are used for deep implants into a substrate. Such deep implants are required to create, for example, retrograde wells. Eaton GSD/HE and GSD/VHE ion implanters are examples of such high-energy implanters. These implanters can provide ion beams at energy levels up to 5 MeV (million electron volts). U.S. Pat. No. 4,667,111, assigned to the assignee of the present invention, Eaton Corporation, and describing such a high-energy ion implanter, is incorporated by reference herein as if fully set forth.
Typically, implants are performed on semiconductor substrates in prescribed series of processes or recipes. Each series may include several recipes, each of which requires a particular level of ion beam current. Current methods of adjusting the ion beam current for different recipes involves an initial tuning of the ion beam source for a particular level of beam current, and then re-tuning the source for any subsequent different level of beam current. Such a method, however, can be time consuming and is most detrimental when beam recipes involving a common species (e.g., boron or phosphorous) are connected in a series chain. The time saved by running recipes in series is offset by the time required to re-tune the source between recipes.
It is known to utilize a variably sized aperture in an ion implanter beamline to allow one or more than one isotope of a desired ion to pass through the aperture and be implanted into a substrate. Such an aperture is shown in U.S. Pat. No. 5,130,552, wherein the aperture size is predetermined for each ion implant process and adjusted accordingly. It is not known, however, to provide such an aperture in a high-energy implantation system. Nor is it known to provide a control circuit for such an aperture using ion beam current feedback to permit dynamic adjustment thereof.
It is an object of the present invention, then, to provide an improved adjustable aperture for use in the beamline of an ion implantation system. It is a further object of the invention to provide such an adjustable aperture for use in a high-energy ion implantation system. It is yet a further object to provide a method of controlling such an adjustable aperture, wherein ion beam current is used as a feedback signal to the control system.